Using Biological Systems
Consequently, a number of themes and similarities of approach exist, which run as common and repeated threads throughout the whole of the science. Thus, optimisation of the activities of particular organisms, or even whole biological communities, to bring about any desired given end, typically requires manipula-tion of local conditions. Control of temperature, the accessibility of nutrients and the availability of oxygen are commonly the tools employed, especially when the target effectors are microbes or isolated biological derivatives. For the kind of whole organism approaches typified by phytotechnological interventions discussed, this may prove a more difficult proposition, but nevertheless, one which still remains relevant at least in principle. The typical factors affecting the use of biological systems in environmental engineering relate to the nature of the substances needing to be removed or treated and to the localised envi-ronmental conditions pertaining to the particular situation itself. Thus, in respect of the former, the intended target of the bioprocessing must generally be both susceptible and available to biological attack, in aqueous solution, or at least in contact with water, and within a low to medium toxicity range. Generally, the local environmental conditions required would ideally offer a temperature of 20 – 30 ◦ C but a range of 0 – 50 ◦ C will be tolerated in most cases, while an optimum pH lies in the range 6.5 – 7.5, but again a wider tolerance of 5.0 – 9.0 may be acceptable, dependent on the precise organism involved. For land-based applications, especially in the remediation of contamination or as a component of integrated pollution control measures, there is an additional common constraint on the substrate. Typically the soil types best suited to biotechnological inter-ventions are sands and gravels, with their characteristically low nutrient status, good drainage, permeability and aeration. By contrast, biological treatments are not best suited to use in clays or peat or other soils of high organic content. In addition, generalised nutrient availability, oxygenation and the presence of other contaminants can all play a role in determining the suitability of biological intervention for any given application.
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